The invention relates to an electromechanic film, which film is dielectric and intended for transforming electric energy into mechanical energy and/or transforming mechanical energy into electric energy in such a way that a voltage or a charge is conducted onto the surfaces of the film, and/or a voltage or a charge is discharged from the surfaces of the film.
Further, the invention relates to an acoustic element comprising two electromechanic films joined to each other.
U.S. Pat. No. 4,654,546 discloses an electromechanic film in which the dielectric material is provided with flat discoid gas bubbles. The film can be charged and metallized. When a voltage is conducted over the film, the force generated by the electric field reduces the thickness of the film, whereby the bubbles flatten, and the air inside the bubbles is pressed and the pressure increases. The thickness of the film is thus capable of changing, but the length and width of the film hardly change at all. The change in the thickness is also rather small. At the maximum voltage, the change in the thickness of the film is only about 0.1% of the thickness of the film. In some applications it would be necessary to achieve a greater change in the dimensions of the film.
An object of this invention is to provide an electromechanic film with improved properties compared with the prior art.
The electromechanic film according to the invention is characterized in that it is formed of cells, the ratio of the height and width of which cells is between 3:1 and 1:3, whereby, when a cell deforms, the pressure resisting the deformation inside the cell remains essentially unchanged.
Further, the acoustic element according to the invention is characterized in that the film is formed of cells, the ratio of the height and width of which cells is between 3:1 and 1:3, and that the acoustic element comprises means for controlling the films in such a way that in the first film the electric field strength decreases and in the second film the electric field strength increases, whereby the joined films in the acoustic element bend.
An essential idea of the invention is that the film is formed of cells, preferably polygonal cells, with thin walls, the ratio of the height and width of which cells is between 3:1 and 1:3. Hereby, when a cell deforms, the pressure resisting the deformation inside the cell changes only a little. The idea of a preferred embodiment is that the cells are elongated in such a way that the ratio of the height and length of the cells is less than 1:3, preferably less than 1:10.
It is an advantage of the invention that when the film is pressed, the cells deform and become wider, and thus the film also becomes wider as the cell walls bend. The longer the cells, the less they resist the deformation of the film.